My car is a 1973 MGB. About five years ago and only 8,000 miles I had a new brake master cylinder installed when I was rebuilding/replacing/restoring everything.

Now, since early spring, if I let my car sit for any period of time - more than a week - when I get in the car there is a small puddle of brake fluid on my floor mat, where it has drained down from the brake pedal from the master cylinder. The master cylinder is leaking through the main rod.

So, it looks like I am going to have to replace the master cylinder and I have a few questions:

1) Where is the best place to get a new master cylinder?
2) Am I going to be able to buy a new one or will it be rebuilt? Does it matter?
3) Can I rebuild mine? I have read in the archives that you should not do this and it is better to replace it.
4) I have worked on American cars all my life and I have replaced many master cylinders. This will be my first one on my MGB. Is changing it the same as an American car? Are there any secrets/tips/tricks I should know?

The only trick is getting the old one out and replacing it with new. It makes it a lot easier if you remove all the bolds holding the pedal box to the body. That will give you enough wiggle room to remove it.

PM Basil Adams. He has new MCs for a good price. You might want to consider replacing the clutch master at the same time as a preventive measure (it's such a hassle that once you're in there....might as well...). British Parts Northwest has 'em for about $60. Others might as well.

You will need to retain the old pushrod, banjo rear connection (new copper washers should be provided with the MC), and the little filter/spring inside the port for the banjo port may also have to be retained from the old one. Check the front port to make sure the filter is there (will require 20mm wrench...why mm? dunno! but it is)

I have taken to redrilling the two mounting holes (and pedal box) and installing 3/8" helicoils so i can use a 3/1 - 3/4" cap screw from the front and not have to wrestle with a nut I can't easily get to.

Don't forget the foam rubber seals (or make a set from cork gasket material...could be cheaper to get the seals. I also replaced the stock screws used to hold down the pedal box and cover with stainless and a little anti-seize. This area is prone to rusting as brake fluid dissolves the paint over time...I'm thinking this might make it easier to remove it in 5 years. Also had to install a 1/4-28 rivnut to replace a hold down weldnut that broke off when removing the screw (rust!).

If you can rebuild an American brake cylinder then you can certainly rebuild an MG brake cylinder.

Most of the people on this BBS seem to have a great fear rebuilding brake cylinders. I suppose I can understand that because so much is riding on a good job. However, the way I look at it, when you buy a rebuilt cylinder, it was rebuilt by some factory worker who is probably no more skilled than you are. You will have to be the judge.

These are not terribly difficult cylinders to rebuild. There is a circlip that is tricky to get out and a plastic washer/spacer that always gets stuck (the manual helpfully says to "tap it out&quot. A new plastic spacer comes with the rebuild kit so you don't worry about destroying it - the only trick is in getting it out without scoring the cylinder.

The bore is small and takes a fairly small hone - the one for a VW bug seems to work well.

Take fastidious notes as to how it comes apart. Use the service manual picture and the Moss exploded diagram. Use lots of brake fluid to assemble the rubber parts.

If you need a new cylinder (yours is rusted or scored) then by all means get one from Basil. If you do not feel competent to rebuild a cylinder, then err on the side of safety. But if you are comfortable rebuilding brake cylinders then you can save a pile of money by doing it yourself.

Hey, don't worry about rebuilding the Master Cylinder. I think that kind of talk comes from people that just don;t realize that the older MGB stuff is usually far superior to anything that's made in the Chinese part of Great Britain.

They're are easy enough to rebuild.

I bet you have a whole mess of left shoes that are far dirtier than the right shoes!

Back about 20 years ago, and for a stretch of about five years, I kept having my left shoe get all dirty all the time. Well, I drove my MGB every single day of the year. The end seal of the brake MC had an itsy bitsy little drip to it. I lost a little fluid here and there, but it was so minute that it never really set off any buzzers in my head.

The thing was, it only dripped when I stepped on the brake pedal, and then not even every time, not even close, so the fluid when it did drip, went onto my left shoe. So I never noticed any wet fluid on the mat at all.

It wasn't until I was installing a stereo, that I had my head way down under there, looking up under the dash, and the back of my head hit the pedals. Well, a little drip fell right in my face. Then I noticed the little bit of moisture at the top of the pedal, and it was finally that I realzied why my left shoes were all getting wrecked for years.

I just rebuilt the one on my 73 GT. I was nervous about doing it, because many on here had said how hard it was.

If you are mechanically inclined and lay things out in the order the come out, it is not difficult. Even removing the circlips down in the cylinder, wasn't that hard.

To get the circlips out, I used 2 long thin pointed tools (don't know what they are, but are like 5" long thin screwdrivers that come to a sharp tapered point, you could even sharpen the points on screwdrivers to fit in the holes on the clips). Use these to reach into the cylinder and pull/pry the ends of the clip together and up. Mine came out really easily.

To get the plastic spacer out, I just tipped the cylinder upside down and tapped it, it fell out, others here have talked about running a screw in to it to give something to grab onto.

The rest is pretty self explanatory. Just pay attention to how you take it apart, keep everything clean and in order, and lube it up with brake fluid as you reassemble.

In the past a number of people who just bought their MGB dream car went about changing all the fluids-oil, transmission oil and brake fluid. They were often sad to find failures in the brake system caused by using the wrong brake fluid. I dont know the situation now, but in the 70's and 80's dot4 LMMA was about the only recommended stuff for the brake system. Other fluids would soften and destroy the seals. I dont know if the materials have changed, but I still use LMMA in my B's and rarely have a problem with the clutch or brake hydraulics.

I rebuilt the brake MC on my daily driver 3 years ago and it has been trouble free in brake-reliant Los Angeles traffic. The hardest part was the 2nd circlip. Long, thin and pointed about describes the tool I made to get it out. Other than that it is a standard job as mentioned in the other posts.

Quote:
In the past a number of people who just bought their MGB dream car went about changing all the fluids-oil, transmission oil and brake fluid. They were often sad to find failures in the brake system caused by using the wrong brake fluid. I dont know the situation now, but in the 70's and 80's dot4 LMMA was about the only recommended stuff for the brake system. Other fluids would soften and destroy the seals. I dont know if the materials have changed, but I still use LMMA in my B's and rarely have a problem with the clutch or brake hydraulics.

Brake fluid all have their drawbacks and positives. All brake systems end up with water in them, simply from condensation. The way this world works and the constant heating and cooling of the brake systems causes condensation inside the pipes. Some of this water is fizzled off thru heat, but it just condenses back down and becomes water again.

If you use the regular old stuff that absorbs water. Well, then it absorbs water. the brake fluid disperses the water throughout the system. But over years and years the amount of water is too much for the fluid and it must be changed. But, there's usually very little damage to metal parts inside. That's pretty self explanatory.

But, if you use the silicone kind that DOESN'T absorb water, then it DOESN'T absorb water and that's even worse. Some say huh? how can that be worse???

Well, if it doesn't absorb water then the water sits, separately from the silicone brake fluid. Well, that water usually finds a nice resting place, right next to some metal part that doesn't like water sitting next to it. Well then you get brake failure. This will also take lots of time.

The bottom line, whatever you end up using, just inspect and change it frequently and you'll head off all problems! By frequently, I mean every few years or so.